1. Technical Field
The present invention relates to a technique for controlling gradation levels of electro-optical elements such as organic light emitting diode (OLED) elements.
2. Related Art
Electro-optical devices having multiple electro-optical elements have been proposed. Each of the electro-optical elements is controlled to a gradation level corresponding to the level (such as the voltage value or the current value) of a data signal output from a driving circuit. The driving circuit generates a data signal having a level corresponding to a gradation value D specified by image data. A characteristic curve FC1 shown in FIG. 19 indicates the relationship between the voltage of the data signal and the gradation of the electro-optical elements (e.g., the brightness of the OLED elements).
JP-A-2003-255900 discloses a display device in which the relationship between a gradation value D and an actual gradation level of an electro-optical element is adjusted by a gamma correction. FIG. 20 is a graph showing the relationship between a gradation value D and a gradation level of an electro-optical element when the gamma value is set to 2.0.
There is a demand for an electro-optical device capable of multiple gradation display. However, the step width of levels of a data signal (that is, the minimum change amount) needs to be reduced to finely change the gradation of electro-optical elements. Therefore, a problem occurs in that a high-performance large-scale driving circuit is needed, resulting in an increase in the cost of the electro-optical device.
The above-described problem becomes noticeable when the luminous efficiency of the electro-optical elements increases. That is, as indicated by a characteristic curve FC2 shown in FIG. 19, the change amount of the gradation of the electro-optical elements with respect to the level (e.g., the voltage value) of the data signal increases as the luminous efficiency of the electro-optical elements increases. Thus, if the gradation of the electro-optical elements changes by a value of ΔG shown in FIG. 19, it is necessary to improve the performance of the driving circuit so that a step width ΔV2 of levels of the data signal becomes smaller than a step width ΔV1 in the characteristic curve FC1.
Further, in a case where the gamma correction is performed using a gamma value higher than 1, as shown in FIG. 20, it is necessary to reduce the step width ΔG of the gradation levels of the electro-optical elements, in particular within a low-gradation range. In this case, it is also necessary to finely change the voltage of the data signal, and there arises a problem of increasing the cost of the electro-optical device.